One conventional class of spectrophotometers is utilized for measuring optical transmission of liquid samples in the spectral range of near infrared to ultraviolet. There are continuing needs for improvements in precision and in ease of incorporating the optics of the instrument into each of a set of sample liquids. Precision in measurements is particularly related to uniformity in pathlength in the optical train at the liquid sample, and minimizing reflection and refraction effects. Mechanically, an optical probe device should be small, portable, reliable and rugged. Fiber optics provide a basis for a suitable probe that may be inserted into liquid samples.
The usual way to sample any one of a number of liquids contained in separate containers is to aspirate the selected liquid from its container into the instrument. Typical examples are described in U.S. Pat. Nos. 4,229,179 (Lee) and 4,222,670 (Koshiishi). The latter patent also illustrates concerns for precision optical surfaces in the system for measuring light transmission of the liquid, and for removing liquid from the optical system in preparation for the next sample. Generally the aspiration method adds time to the process and requires significant channeling susceptible of contamination by prior liquids.
U.S. Pat. No. 4,431,307 (Suovanieme) teaches arranging the liquid containers ("cuvettes") in a matrix, with each container having its own optics. The use of optical fibers immersed in liquid is disclosed in U.S. Pat. No. 4,403,861 (Boisde et al), apparently with a simple gap between fiber ends for passing light through a portion of the liquid This approach potentially solves some of the above problems but does not address any need or method for incorporating precision optics into the liquid.
An object of the invention is to provide a novel optical probe for insertion into liquids for measurement of light transmission characteristics of the liquid by a photospectrometer. A further object is to provide such an optical probe having improved optical precision. Another object is to provide such a probe that is small, portable, reliable and rugged.